Printing using catalytic inks has been practiced for producing patterns which are catalytic to electroless deposition for producing a variety of products including printed circuitry and decorative metal patterns. Typically catalytic inks contain a metal for catalyzing electroless deposition, e.g. copper, silver or a noble metal such as palladium. Such inks are used to produce catalytic patterns on a non-conductive substrate, e.g. by screen printing, by lettering from a felt tip pen, by ink-jet processes and the like. The metal components for catalytic inks have been in a variety of physical forms, e.g. dissolved salts, colloidal hydrosols, and particulates such as powder or flake. The inks have a wide range of rheological properties depending on the intended method of application. For instance, inks for application by ink-jet have especially low viscosity and consist essentially of palladium salt in an organic solvent. Inks for screen printing have especially high viscosity, e.g. are referred to as pastes, and consist typically of polymer binder and particulate metal.
The following patent publications disclose the production of printed circuit boards by electroless deposition on a catalytic ink pattern. EPO publication 0 132 677 discloses low viscosity ink (e.g. 0.3-100 cp) comprising a catalytic metal solution which is applied to a surface by an ink-jet or ink-mist process.
In U.S. Pat. Nos. 4,493,861 and 4,622,411 a catalytic pattern is formed by spraying through a template a palladium-containing alkyl resin solution; the patterned resin is hardened for 5 hours then electrolessly deposited with nickel. U.S. Pat. No. 4,622,411 also discloses the silk screen printing of palladium-containing prepolymer which is cured for 8 hours prior to electroless deposition of nickel.
In U.S. Pat. No. 4,322,457 catalytic patterns are formed by printing a surfactant ink which is dried, treated with a sensitizing agent, e.g. a tin salt, then catalyzed by treating with a palladium solution.
In U.S. Pat. No. 3,745,045 catalytic inks are based on epoxy paint containing metal flakes, e.g. of nickel or aluminum.
Screen printing of catalytic patterns requires the use of pastes having high viscosity due to high solids levels and particulates. Because of their viscosity such pastes typically have long drying times, e.g. at least about 1 hour. For instance, in U.S. Pat. No. 4,248,921 the paste comprises metal particles, metal salt and polymer; in U.S. Pat. No. 4,469,714 the paste comprises a thermosetting or U.V. curable resin containing finely divided palladium catalyst; in U.S. Pat. No. 4,832,989 pastes comprise copolymer binder, palladium compounds and inorganic particulate such as aerosols, titanium dioxide, talc and the like and illustrative pastes dry in about 1 hour at 100.degree. C.; in British Patent Specification 938,365 high viscosity (i.e. 200 poise) catalytic inks comprise phenolic resin, powdered metal (e.g. aluminum) and powdered silica; in Canadian Patent 1,271,374 pastes comprise a palladium compound and inorganic filler in a polyurethane solution and illustrative pastes dry in about 1 hour at 150.degree. C.; in PCT publication WO 88/02592 pastes comprise copolymer binder, inorganic particulate and palladium compounds and illustrative pastes dry in about 30 minutes at 150.degree. C.; in PCT publication WO 87/04190 high viscosity (15,000-200,000 cp) inks comprise polymer and metallic powder; and in U.S. Pat. No. 4,670,351 high viscosity (15,000 to 200,000 cp) inks comprise curable silicone and finely divided metal powder.
Japanese Kokai 59038370 discloses catalyst of fine metal powder in a polymeric binder; Japanese Kokai 62207878 discloses catalytic paste containing a palladium hydrosol, a surfactant and a water soluble binder; Japanese Kokai 62078179 discloses printing paste of high melt point metal powders; and Japanese Kokai 63270474 discloses aqueous catalytic ink comprising 0.2-0.8 wt % silver salt, 40-60 wt % starch base binder, 0.2-1.3 wt % silane coupling agent and 0.5-3.5 wt % sulfur compound.
Despite the variety of printing inks and techniques disclosed as useful for producing printed circuitry and other conductive metal devices, a major deficiency is the slow speed of the methods. For instance, the disclosed screen printing is typically carried out on stationary substrates using slow drying paste requiring a large holding area to dry the printed image. Although screen printing can be applied to a moving web, such processing is impractical due to the slow drying associated with typically disclosed pastes. Moreover, such pastes typically contain high levels of particulate solids which preclude the use of pastes for fine imaging. Although low viscosity inks are disclosed, the associated printing techniques, e.g. spraying through a template or ink-jet printing, are not typically fast when applied to moving webs.
Many of the problems of the prior art are overcome by the high speed printing methods of U.S. Pat. No. 4,368,281 which discloses the production of flexible printed circuits having line widths as little as 10 mils (250 micrometers) using a variety of printing techniques, e.g. flexographic, silk screen, intaglio, at speeds of 25-260 ft/min (8-80 meters/min) using a catalytic printing ink containing 12-15 percent by weight solids (palladium complex, a polymeric resin adhesive, pigment filler and crosslinking agent) and up to 88 percent by weight solvent. Depending on the printing technique, ink viscosity is adjusted e.g. 4000 cp for screen printing, 300-1200 for flexographic printing and 80-350 cp for intaglio printing, using a variety of fillers, preferably ferric oxide, or fast evaporating solvents, e.g. trichloroethane. It is disclosed that the ink should contain 8-15 weight percent filler. After drying in a hot (80.degree.-110.degree. C.) air blast, the ink is crosslinked by baking at 90.degree.-100.degree. C. for about a minute. Intaglio printing utilizes an engraved roll in which the web is deformed into the cavities to contact ink.
An object of this invention is to provide a improved method for fabricating articles such as printed circuits by electroless deposition on catalytic images formed on moving webs traveling at high speeds, e.g. up to 500 meters/minute, using catalytic inks comprising low levels of solids comprising polymer and catalytic metal.
Another object of this invention is to provide a method for printing on moving webs catalytic images in fine line widths, e.g. less than 100 micrometers, and as narrow as about 25 micrometers, which can be metal plated for utility as electrical, electronic, energy conversion and/or mechanical devices.
Still another object of this invention is to provide continuous methods of printing, drying and activating images of catalytic ink on moving webs and plating metal on the activated-imaged moving web.
These and other objects that will be apparent from the advantages described in the following specification and illustrative examples are met by the invention set forth in the following claims for methods of producing articles using catalytic inks.